<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a=10;
        var b=20;
        function swap(a,b){
            var temp=a;
            a=b;
            b=temp;
        }
        swap(a,b);
        console.log(a,b); //10,20
    </script>
</body>
</html>